1. Field of the Invention
This invention relates to a vehicle, particularly to a tracklaying vehicle, which comprises a driving and steering mechanism comprising a drive motor, which has a motor shaft that is parallel to and extends beside the vertical longitudinal center plane of the vehicle, a shiftable transmission, which operatively connects said shaft to a power train, which comprises an angle drive and a universal-joint shaft, two planetary spur gear trains for driving respective propelling wheels of the vehicle and adapted to be driven by said power train, and a controllable hydrostatic transmission, which is operatively connected to said drive motor and arranged to rotate two gear members of respective ones of said planetary spur gear trains in mutually opposite senses.
2. Description of the Prior Art
Vehicles provided with such driving and steering mechanisms are already used in practice. In the known mechanisms, the shiftable transmission extends beside the drive motor and is driven via a plurality of spur gears from that end of the motor which is opposite to the propelling wheels. In a direction which is approximately parallel to the motor shaft, the power train extends from the output shaft of that shiftable transmission to the two planetary spur gear trains, which are directly driven by the angle drive, which is connected to the shiftable transmission by the universal-joint shaft. The pump of the hydrostatic transmission is driven by the drive motor from that end thereof which faces the propelling wheels, also via a universal-joint shaft and an intermediate transmission. The controllable hydrostatic transmission rotates two gear members of respective ones of the planetary spur gear trains in mutually opposite senses and is used to steer the vehicle because the two propelling wheels are rotated at different speeds as one gear member of each planetary spur gear train is driven in a sense that is opposite to the sense of rotation of the corresponding gear member of the other planetary spur gear train whereas the other gear members of the planetary spur gear trains are driven by the drive motor via the power train in the same sense. As a result, the track chain provided on one side of the vehicle leads or lags the track chain provided on the other side of the vehicle.
In the known arrangement, in which the shiftable transmission extends beside the drive motor and is connected to the latter by spur gears, the mechanism has approximately the shape of a U, which can be mounted only with difficulty and which is undesirable from a static aspect. For this reason a heavy and relatively rigid structure is required. The spur gears for transmitting power from the motor to the shiftable transmission increase the structural expenditure, which is increased further by the universal-joint shaft and the intermediate transmission used to drive the pump of the hydrostatic transmission, particularly because a relatively high power is required for that pump. It will be understood that the large number of idler wheels which are required will adversely affect the efficiency of the entire mechanism and will contribute to the temperature rise of the lubricating oil, so that a larger oil cooler or an additional oil cooler is required. A further disadvantage resides in that the universal-joint shaft of the power train and the shafts which drive said universal-joint shaft and are driven by it are in most cases not axially aligned but extend at certain angles to each other so that transverse forces are exerted, which must be taken up by the structure provided to mount the motor-transmission unit.